The present invention relates to a multi-channel magnetoresistance effect (MR) type magnetic head for a digital audio tape recorder (hereinafter referred to as "DAT"), for example.
In a multi-channel MR type magnetic head for a DAT, a magnetic head element corresponding to a number of data tracks, a magnetic head element corresponding to tracks where graphic character information or the like is recorded and reproduced individually (hereinafter referred to as "AUX tracks"), and a magnetic head element corresponding to tracks for enabling high-speed random access, i.e. cue tracks which permit a speed variation and reading in forward and reverse directions and contain time record information, music number information or the like (hereinafter referred to as "CUE tracks"), are arranged
Among these tracks, in the data track and the AUX track, the recording is performed at a short wavelength region (hereinafter referred to as "first wavelength region") to increase the recording density. In the CUE track, however, the recording is performed at a long wavelength region (hereinafter referred to as "second wavelength region") with a considerably longer wavelength than that of the first wavelength region so as to read the signal in a secure fashion, even if the spacing is increased during the high-speed search.
In such a prior art magnetic head, each magnetic head element corresponding to the various tracks is manufactured in the same process to simplify the manufacturing and designing of the magnetic head element, which is selected to provide the best characteristics in the magnetic head element of the data track necessitating the particular sensitivity. First, a multi-channel MR type magnetic head of the prior art will be described
FIGS. 6 and 7 respectively show a schematic plan view and a sectional view of a multi-channel MR type magnetic head of the prior art. In the magnetic head, a magnetic substrate 1 is made of Ni-Zn ferrite, for example, and a bias conductor 2 of a band-shaped conductive film as a current path for supplying a bias magnetic field to MR sensing element corresponding to each channel, i.e. each track is formed on the magnetic substrate 1 linearly along the arranged direction of each channel. MR sensing elements MR.sub.aux, MR.sub.cue, and MR made of Ni-Fe alloy or Ni-Co alloy thin film, and corresponding to respective channels, i.e. AUX tracks, CUE tracks, and data tracks, are formed on the bias conductor 2 through an insulation layer 3. A front magnetic core 6 and a back magnetic core 7, each formed of a magnetic layer of Ni-Fe alloy for example, are also formed on the MR sensing elements with an insulation layer 5 in the direction crossing the MR sensing elements MR.sub.aux, MR, MR.sub.cue corresponding to respective channels. These cores 6 and 7 are spaced on the sensing elements MR.sub.aux, MR, MR.sub.cue at a discontinuity portion G for a required distance. An outside edge of the front magnetic core 6 is adjacent to and faces the magnetic substrate 1 through a non-magnetic insulation layer. The gap spacer 4, and a magnetic gap (g) with a gap length defined by the gap spacer 4, is formed between the core 6 and the magnetic substrate 1. The gap spacer 4 may be formed by the insulation layer 5 and/or the insulation layer 3, or otherwise it may be formed by etching the layers 5, 3 in a partial thickness or by newly forming other non-magnetic layers. Its width is selected to provide a gap depth (d) for the magnetic gap (g). An outside edge of the back magnetic core 7 is connected through a window 8, for example, bored on the insulation layers 3 and 5, to the magnetic substrate 1 in close magnetic coupling. A non-magnetic insulation protective layer 9 is formed to cover the bias conductor 2, the MR sensing elements MR.sub.aux, MR, MR.sub.cue, and the magnetic cores 6 and 7, and a protective substrate 11 is adhered onto the non-magnetic insulation protective layer 9 by an adhesive agent layer 10. An outside edge of the substrates 1 and 11 and the front magnetic core 6 between these substrates is commonly cut and polished a surface 12 opposite to the magnetic medium is thus formed Accordingly, the magnetic gap (g) faces on the opposite surface 12, and magnetic head element units h.sub.aux, h.sub.cue corresponding to the AUX and CUE tracks and data track magnetic head element unit h, each have a closed magnetic path formed by the magnetic substrate 1 - the magnetic gap (9) - the front magnetic core 6 -the MR sensing elements MR.sub.aux, MR, MR.sub.cue - the back magnetic core 7 - and the magnetic substrate 1.
In such a construction, through conduction in the bias conductor 2, the bias magnetic field is supplied to the MR sensing elements MR.sub.aux, MR.sub.cue, MR, thereby detecting current flows in each of the MR sensing elements MR.sub.aux, MR.sub.cue, MR. A resistance variation based on the magnetic field variation in each of the closed magnetic paths leading to the MR sensing elements MR.sub.aux, MR.sub.cue, MR by the recorded electric field on the magnetic medium is detected as a voltage variation, for example, and reproduced.
In the multi-channel MR type magnetic head as above described, a track width W.sub.cue of the magnetic head element unit h.sub.cue for the CUE tracks is selected larger than a track width W in the other magnetic head element unit, and each of the MR sensing elements MR.sub.aux, MR.sub.cue, and MR, and hence each discontinuity portion G, is arranged linearly along the arranging direction of each of the magnetic head element units h.sub.aux, h.sub.cue, and h, i.e. at an equal distance L from the opposite surface 12 to the magnetic medium. A width of the gap spacer 4 to define the gap depth is selected equal in each of the magnetic head element units h.sub.aux, h.sub.cue and h, and the gap depth of each magnetic gap (g) of the element units h.sub.aux, h.sub.cue and h is selected to a constant depth (d).
A forward travelling direction of the magnetic medium relative to the magnetic head is selected in the direction along the width direction of the magnetic head as shown by arrow (a) in FIG. 7, e.g. in the direction from the protective substrate 11 towards the magnetic substrate 1.
In such a multi-channel MR type magnetic head, the magnetic head element unit h.sub.cue to the CUE tracks has the same construction and hence the same characteristics as that of the other magnetic head element unit h for data tracks. In this case, in order to perform the best reproduction in the data track as described at the beginning, in a construction thereof, i.e. at the gap depth (d) of the magnetic head (g), a distance between the opposite surface to the magnetic medium and the MR sensing element (i.e. substantial length L of the front magnetic core), the gap length, and the core thickness or the like, may be selected.
In the multi-channel MR type magnetic head as above described, problems may result at long wavelength regions, i.e. the second wavelength region, and more specifically at the magnetic head element unit h.sub.cue for the CUE tracks. In the MR type magnetic head of a so-called yoke form where the front magnetic core 6 and the back magnetic core 7 are installed, and the MR sensing element is arranged at the discontinuity portion G between both cores, since the substantial length L and the thickness of the front magnetic core 6 are finite, a magnetic flux at a long wavelength from the magnetic medium cannot be entirely taken into the magnetic path leading to the MR sensing element. In other words, the deterioration of long wavelength reproduction output characteristics and the phase rotation in the long wavelength region are an inherent property based on a structure of the magnetic head. Particularly in each MR type magnetic head element as above described, since the substantial length of the front magnetic core 6 in each magnetic head element, i.e. distance L between the opposite surface 12 to the magnetic medium and the MR sensing elements MR.sub.aux, MR.sub.cue, MR, is selected as a small value so as to obtain good output characteristics in the long wavelength region, a deterioration of the reproduction output characteristics and the phase rotation in he output waveform, and a so-called dullness of the waveform. This disturbs the signal reading on the CUE track. Consequently, problems may be produced particularly when reading during a reverse feeding of the magnetic medium.
When all magnetic head elements for data tracks and CUE tracks are made with the same characteristics, since the transmission characteristics in the magnetic head naturally show the higher transfer function at the long waveform region, problems may be produced by a non-linear action in the MR sensing element caused by excessive input to the CUE track at the long wavelength reproduction. Furthermore, since a distance L between the opposite surface to the magnetic medium and the MR sensing element is selected as a small value as above described, rubbing noise problems may be produced during the high-speed search. The rubbing noise is caused by a heating of the MR sensing element by the flowing detecting current. This heat is radiated in unstable fashion by the unstable contacting during the high-speed travelling of the magnetic medium of the magnetic head. For example, if the reproduction output from the CUE track has a noiseless waveform as shown in FIG. 8A and the detecting data train has a rectangular waveform as shown in FIG. 8B, the detecting waveform producing the rubbing noise shows a variation of a d.c. level of the low region noise caused by the rubbing noise as shown in FIG. 9A. Thus, the waveform variation causes a jitter of the detecting data as shown in FIG. 9B.